Method and apparatus for encoding and decoding video signal using motion compensation based on affine transformation

ABSTRACT

A video encoding method and apparatus are provided. The video encoding method includes determining whether a current block includes an affine-transformation object having an affine transformation; if the current block includes an affine-transformation object, generating a prediction block by performing affine transformation-based motion compensation on the current block in consideration of an affine transformation of the affine-transformation object; and if the current block does not include any affine-transformation object, generating a prediction block by performing motion vector-based motion compensation on the current block using a motion vector of the current block. Therefore, it is possible to achieve high video encoding/decoding efficiency even when a block to be encoded or decoded includes an affine transformation.

TECHNICAL FIELD

The present invention relates to a video encoding method and apparatusand a video decoding method and apparatus in which a video signal can beencoded through affine transformation-based motion compensation.

The present invention is based on research (Project Management No.:2007-S-004-01, Project Title: Development of Rich Media BroadcastingTechnology through Advancement of AV codec) conducted as part ofInformation Technology (IT) Growth Power Technology Development Projectlaunched by Ministry of Information and Communication and Institute forInformation Technology Advancement (IITA).

BACKGROUND ART

Inter-frame encoding such as H.264 video encoding is similar to othervarious video encoding methods in terms of predicting a current blockthrough block-oriented motion estimation and encoding the predictedcurrent block. However, inter-frame encoding is differentiated fromother various video encoding methods by using various macroblock modesand adopting different block sizes for the various macroblock modes soas to perform motion estimation and motion compensation. Inter-frameencoding generally includes performing motion estimation in each of thevarious macroblock modes, choosing whichever of the various macroblockmodes is determined to be optimal in consideration of rate-distortionperformance, and encoding a prediction error in the chosen macroblockmode, i.e., the difference(s) between a current block and a blockobtained by performing motion estimation on the current block.

In inter-frame encoding, like in other various video encoding methods,motion estimation and motion compensation are performed only inconsideration of horizontal and vertical translational motioncomponents. That is, referring to FIG. 1, motion estimation and motioncompensation may be performed on a current block only in considerationof horizontal and vertical motions (mv_(x) and mv_(y)) with respect to areference frame.

If motion estimation and motion compensation are performed only inconsideration of horizontal and/or vertical motions, coding complexitymay decrease, but it may not be able to achieve high encoding efficiencyespecially when an object in a picture to be encoded has an affinetransformation such as rotation, enlargement or reduction. On the otherhand, if motion estimation and motion compensation are performed inconsideration of all possible transformations of an object, encodingefficiency may increase, but coding complexity, and particularly, thecomplexity of motion estimation, may considerably increase.

DISCLOSURE OF INVENTION Technical Problem

The present invention provides a video encoding method and apparatus anda video decoding method and apparatus which can achieve high encodingefficiency even when a block to be encoded includes anaffine-transformation object having an affine transformation such asrotation, enlargement or reduction.

Solution to Problem

According to an aspect of the present invention, there is provided avideo encoding method including determining whether a current blockincludes an affine-transformation object having an affinetransformation; if the current block includes an affine-transformationobject, generating a prediction block by performing affinetransformation-based motion compensation on the current block inconsideration of an affine transformation of the affine-transformationobject; and if the current block does not include anyaffine-transformation object, generating a prediction block byperforming motion vector-based motion compensation on the current blockusing a motion vector of the current block.

According to another aspect of the present invention, there is provideda video encoding apparatus including a motion estimation unitcalculating a motion vector of a current block with reference to areference block; an affine-transformation object calculation unitdetermining whether a current block to be subjected to motioncompensation includes an affine-transformation object having an affinetransformation and outputting an affine-transformation object detectionsignal corresponding to the results of the determination; and a motioncompensation unit generating a prediction block by performing eitheraffine transformation-based motion compensation or motion vector-basedmotion compensation on the current block in response to theaffine-transformation object detection signal.

According to another aspect of the present invention, there is provideda video decoding method including determining whether anaffine-transformation object exists in a reference block; if anaffine-transformation object exists in the reference block, generating apredicted block by performing affine transformation-based motioncompensation on the reference block; and if no affine-transformationobject exists in the reference block, generating the predicted block byperforming motion vector-based motion compensation on the referenceblock.

According to another aspect of the present invention, there is provideda video decoding apparatus including an affine-transformation objectdetection unit determining whether an affine-transformation objectexists in a reference block and outputting a signal indicating theresults of the determination; a motion compensation unit generating apredicted block by performing one of affine transformation-based motioncompensation and motion vector-based motion compensation on thereference block in response to the signal output by theaffine-transformation object detection unit; and an adding unit whichgenerates a current block by adding the predicted block and a residualsignal.

According to another aspect of the present invention, there is provideda computer-readable recording medium having recorded thereon a programfor executing a video encoding method including determining whether acurrent block includes an affine-transformation object having an affinetransformation; if the current block includes an affine-transformationobject, generating a prediction block by performing affinetransformation-based motion compensation on the current block inconsideration of an affine transformation of the affine-transformationobject; and if the current block does not include anyaffine-transformation object, generating a prediction block byperforming motion vector-based motion compensation on the current blockusing a motion vector of the current block.

According to another aspect of the present invention, there is provideda computer-readable recording medium having recorded thereon a programfor executing a video decoding method including determining whether anaffine-transformation object exists in a reference block; if anaffine-transformation object exists in the reference block, generating apredicted block by performing affine transformation-based motioncompensation on the reference block; and if no affine-transformationobject exists in the reference block, generating the predicted block byperforming motion vector-based motion compensation on the referenceblock.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, affine transformation-based motionestimation/compensation may be performed on each block including anaffine-transformation object having an affine transformation. Thus, itis possible to overcome the shortcomings of conventional video encodingand decoding methods in which motion estimation and motion compensationprediction are preformed in units of blocks only in consideration oftranslational motions. Therefore, it is possible to prevent theperformance of encoding from deteriorating even when an object in ablock to be encoded rotates, the size or shape of the object changes orthere is camera movement.

In addition, according to the present invention, it is possible toestablish an affine model only based on the motion in apreviously-encoded macroblock. Thus, the present invention can bereadily applied to an encoding apparatus (such as an H.264 encodingapparatus) performing encoding in units of macroblocks.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a diagram for explaining conventional motionestimation and compensation methods in which only horizontal andvertical translational motions are considered;

FIG. 2 illustrates a diagram for explaining a typical inter-frameencoding method;

FIG. 3 illustrates a block diagram of a video encoding apparatusaccording to an exemplary embodiment of the present invention;

FIG. 4 illustrates a diagram for explaining a video encoding methodaccording to an exemplary embodiment of the present invention;

FIG. 5 illustrates a diagram for explaining how to divide an 8×8 blockinto eight triangular blocks;

FIG. 6 illustrates a diagram for explaining motion vectors used todeduce an affine transformation at each of a plurality of triangularblocks in an 8×8 block; and

FIGS. 7 and 8 illustrate diagrams for affine transformations that can beused in the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will hereinafter be described more fully withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown.

FIG. 2 illustrates a diagram for explaining a typical inter-frameencoding method. Referring to FIG. 2, the typical inter-frame encodingmethod may largely involve four phases: Phases 1 through 4.

Phases 1 and 2 may be phases for estimating motion. More specifically,in phase 1, a motion vector for each of an inter 16×16 block, inter 16×8blocks, inter 8×16 blocks may be estimated. In phase 2, a motion vectorfor each of a plurality of sub-blocks of an inter 8×8 block, i.e., amotion vector for each of an inter 8×8 block, inter 8×4 blocks, inter4×8 blocks, and inter 4×4 blocks may be estimated.

In phase 3, a sub-macroblock mode may be chosen for a sub-macroblock inan inter 8×8 macroblock by using a rate-distortion function. Therate-distortion function may be represented by Equation (1):

RD cos t=Distortion+λ·Rate  (1)

where Rate indicates a bitrate used to encode side information such as aprediction error (i.e., the differences between a block currently beingencoded and a restored block obtained by compensation using a motionvector of the current block) and a motion vector and Distortionindicates the sum of the squares of the differences between the currentblock and the restored block.

In phase 4, an optimum macroblock mode may be chosen from all macroblockmodes available, including a skip mode and an intra macroblock mode, inconsideration of rate-distortion performance.

In video encoding and decoding methods according to the presentinvention, unlike in the typical inter-frame encoding method, affinetransformation-based motion compensation may be applied only to phases 3and 4 in consideration of coding complexity. That is, in the videoencoding and decoding methods according to the present invention, onlyhorizontal and vertical translational motions may be taken intoconsideration during the estimation of a motion vector, and affinetransformation-based motion compensation, in which the rotation,enlargement or reduction of an object is considered, may be performed inthe phase of motion compensation. Therefore, it is possible to minimizecoding complexity and provide high encoding efficiency.

More specifically, in the video encoding and decoding methods accordingto the present invention, affine transformation-based motioncompensation may be performed only on blocks that are believed toinclude affine transformations such as rotation, enlargement andreduction. Thus, it is possible to minimize coding complexity. Inaddition, the video encoding and decoding methods according to thepresent invention suggest ways to skip an inverse matrix calculationprocess for deducing an affine model from blocks to be subjected toaffine transformation-based motion compensation. Therefore, it ispossible to achieve high encoding efficiency with less computation.

FIG. 3 illustrates a block diagram of a video encoding apparatusaccording to an exemplary embodiment of the present invention. Referringto FIG. 3, the video encoding apparatus may include a motion estimationunit 110, an affine-transformation object calculation unit 120 and amotion compensation unit 130.

The motion estimation unit 110 may calculate a motion vector of acurrent block based on a reference block. The affine-transformationobject calculation unit 120 may determine whether the current blockincludes an affine-transformation object. The motion compensation unit130 may generate a prediction block by compensating for the currentblock based on an affine-object-detection signal provided by theaffine-transformation object calculation unit 120 or the motion vectorprovided by the motion estimation unit 110. The video encoding apparatusmay also include an encoding unit (not shown) generating a bitstream byencoding a differential signal generated based on the difference(s)between the current block and the prediction block and a signalincluding side information such as the motion vector of the currentblock.

FIG. 4 illustrates a diagram for explaining a video encoding methodaccording to an exemplary embodiment of the present invention. Referringto FIG. 4, the video encoding method may be largely divided into twophases: phases 1 and 2 (200 and 220). In phase 1 (200), theaffine-transformation object calculation unit 120 may determine whethera current block includes an affine-transformation object. Phase 2 (220)may involve compensating for the current block through affinetransformation-based motion compensation using information such as themotion vectors of blocks adjacent to the current block (221) if it isdetermined in phase 1 that the current block includes anaffine-transformation object; and performing typical motion compensationon the current block (223) if it is determined in phase 1 that thecurrent block does not include any affine-transformation object.

More specifically, phase 1 (200) may involve determining whether thecurrent block includes an affine-transformation object having an affinetransformation based on the motion vector of the current block and themotion vectors of blocks adjacent to the current block, a referenceframe and macroblock mode information used to encode the current block.

There are two conditions for determining whether the current blockincludes any affine-transformation object: if the maximum of the anglesbetween the motion vector of the current block and the motion vectors ofblocks adjacent to the current block is within a predefined range; andif a maximum variation obtained by applying affine transformation-basedmotion compensation is less than a reference value. If the current blocksatisfies neither the first nor second condition, the current block maynot be subjected to affine transformation-based motion compensation.

Even if the current block includes an affine-transformation object, thecurrent block may not be subjected to affine transformation-based motioncompensation if at least one of the blocks adjacent to the current blockis intra-encoded, if the current block is located on the upper leftcorner of a corresponding frame or if the current block references adifferent reference frame from the blocks adjacent to the current block.

In short, it may be determined whether the current block includes anaffine-transformation object based on the first and second conditions.Thereafter, it may be determined whether to apply typical motioncompensation or affine transformation-based motion compensation to thecurrent block based on whether the current block includes anaffine-transformation object.

In the exemplary embodiment of FIG. 4, video encoding or decoding may beperformed in units of 8×8 blocks. If it is determined in phase 1 thatthe current block has an affine-transformation object, affinetransformation-based motion compensation may be performed on the currentblock by using only the motion vectors within a range that establishescausality. Therefore, it is possible to address the problems associatedwith two-pass coding such as high coding complexity.

Referring to FIG. 5, an 8×8 block may be divided into eight triangularblocks 300 through 307. The triangular blocks 300 through 307 may bemotion-compensated using different affine models.

FIG. 6 illustrates motion vectors used to deduce an affine model foreach of a plurality of triangular blocks in an 8×8 block. Referring toFIG. 6, the affine model for each of a plurality of triangular blocks(i.e., blocks 0 through 7) in a current (8×8) block may vary accordingto a macroblock mode of the current block and a macroblock mode of anumber of blocks adjacent to the current block. If the current block islocated at the lower right corner of a macroblock and the macroblockmode of the current block is a 16×16 mode, the motion vectors of blocks0 through 7 may all be the same. The affine models for blocks 0 through7 may all include translations only and may thus have the same modelformula.

An affine transformation formula between (x,y) and (x′, y′) may berepresented by Equation (2):

$\begin{matrix}{\begin{bmatrix}x^{\prime} \\y^{\prime} \\1\end{bmatrix} = {{\begin{bmatrix}a & b & c \\d & e & f \\0 & 0 & 1\end{bmatrix}\begin{bmatrix}x \\y \\1\end{bmatrix}}.}} & (2)\end{matrix}$

A total of six equations may be required to determine the values ofparameters a, b, c, d, e and f in Equation (2). For this, at least threedisplacement values for (x, y) may be required. If there are more thanthree displacement values, a least square solution may be used todetermine the values of parameters a, b, c, d, e and f in Equation (2).If (x0, y0), (x1, y1), (x2, y2), (x′0, y′0), (x′1, y′1), and (x′2, y′2)are provided as displacement values for (x, y), the values of theparameters a, b, c, d, e and f may be determined using Equations (3):

$\begin{matrix}{{p^{T} = {A^{- 1} \cdot b^{T}}}{where}{A = \begin{bmatrix}x_{0} & y_{0} & 1 & 0 & 0 & 0 \\x_{1} & y_{1} & 1 & 0 & 0 & 0 \\x_{2} & y_{2} & 1 & 0 & 0 & 0 \\0 & 0 & 0 & x_{0} & y_{0} & 1 \\0 & 0 & 0 & x_{1} & y_{1} & 1 \\0 & 0 & 0 & x_{2} & y_{2} & 1\end{bmatrix}}{p = \begin{bmatrix}a & b & c & d & e & f\end{bmatrix}}{b = {\begin{bmatrix}x_{0}^{\prime} & x_{1}^{\prime} & x_{2}^{\prime} & y_{0}^{\prime} & y_{1}^{\prime} & y_{2}^{\prime}\end{bmatrix}.}}} & (3)\end{matrix}$

In the video encoding and decoding methods according to the presentinvention, an affine model for each of a plurality of triangular blocksin an 8×8 block may be deduced using variations at the apexes of each ofthe triangular blocks. Referring to Equations (3), there is no need tocalculate the inverse matrix of matrix A, i.e., A⁻¹, because the inverse6×6 matrix A⁻¹ can be easily obtained from eight inverse matricesrespectively corresponding to blocks 0 through 7, which are allcalculated in advance. Thus, it is possible to reduce coding complexity.

FIG. 7 illustrates the case in which a current block to be encodedincludes an object which is reduced by ½ with respect to the verticalaxis of a previous frame and is inclined to the right at an angle of 45degrees.

Three points of displacement for obtaining an affine model for block 0of a current block are (x₀,y₀)→(x₀+mv_(x0), y₀+mv_(y0)), (x₁,y₁)→(x₁+mv_(x1), y₁+mv_(y1)), and (x₂,y₂)→(x₂+mv_(x2), y₂+mv_(y2)).According to existing video encoding standards as H.264, the minimumsize of macroblocks that can have a motion vector is 4×4. Therefore,motion vectors mvx0 through mvx2 may be different from one another.However, assume that all 4×4 blocks in the current block have the samemotion vector if the minimum size of macroblocks that can have a motionvector is 4×4 in blocks adjacent to the current block.

An affine model for block 0 may be obtained using the three points ofdisplacement, as indicated by Equations (4):

$\begin{matrix}{{p^{T} = {A^{- 1} \cdot b^{T}}}{where}{A = \begin{bmatrix}x_{0} & y_{0} & 1 & 0 & 0 & 0 \\x_{1} & y_{1} & 1 & 0 & 0 & 0 \\x_{2} & y_{2} & 1 & 0 & 0 & 0 \\0 & 0 & 0 & x_{0} & y_{0} & 1 \\0 & 0 & 0 & x_{1} & y_{1} & 1 \\0 & 0 & 0 & x_{2} & y_{2} & 1\end{bmatrix}}{p = \begin{bmatrix}a & b & c & d & e & f\end{bmatrix}}{b = {\begin{bmatrix}{x_{0} + {mv}_{x\; 0}} & {x_{1} + {mv}_{x\; 1}} & {x_{2} + {mv}_{x\; 2}} & {y_{0} + {mv}_{y\; 0}} & {y_{1} + {mv}_{y\; 1}} & {y_{2} + {mv}_{y\; 2}}\end{bmatrix}.}}} & (4)\end{matrix}$

Referring to Equations (4), matrix A includes the coordinates of thecurrent block and the coordinates of each of the blocks adjacent to thecurrent block. If the point (x₀,y₀) is mapped to the origin (0,0),matrix A can be commonly applied to blocks 0 through 7 regardless of theposition of the current block in a corresponding macroblock.

Equations (4) may be transformed into Equations (5), and Equations (6)may be obtained by applying (x1,y1) to Equations (5). Equations (5) andEquations (6) are as follows:

$\begin{matrix}{{p^{T} = {A^{- 1} \cdot b^{T}}}{where}{A = \begin{bmatrix}0 & 0 & 1 & 0 & 0 & 0 \\0 & {- 16} & 1 & 0 & 0 & 0 \\16 & 0 & 1 & 0 & 0 & 0 \\0 & 0 & 0 & 0 & 0 & 1 \\0 & 0 & 0 & 0 & {- 16} & 1 \\0 & 0 & 0 & 16 & 0 & 1\end{bmatrix}}{p = \begin{bmatrix}a & b & c & d & e & f\end{bmatrix}}{{b = \begin{bmatrix}{mv}_{x\; 0} & {mv}_{x\; 1} & {{mv}_{x\; 2} + 16} & {mv}_{y\; 0} & {y_{1} - 16} & {mv}_{y\; 2}\end{bmatrix}};{and}}{p^{T} = {B \cdot b^{T}}}} & (5) \\{{where}{B = {\frac{1}{16} \cdot \begin{bmatrix}{- 1} & 0 & 1 & 0 & 0 & 0 \\1 & {- 1} & 0 & 0 & 0 & 0 \\16 & 0 & 0 & 0 & 0 & 0 \\0 & 0 & 0 & {- 1} & 0 & 1 \\0 & 0 & 0 & 1 & {- 1} & 0 \\0 & 0 & 0 & 16 & 0 & 0\end{bmatrix}}}{p = \begin{bmatrix}a & b & c & d & e & f\end{bmatrix}}{b = {\begin{bmatrix}{mv}_{x\; 0} & {mv}_{x\; 1} & {{mv}_{x\; 2} + 16} & {mv}_{y\; 0} & {y_{1} - 16} & {mv}_{y\; 2}\end{bmatrix}.}}} & (6)\end{matrix}$

According to the H.264 standard, motion estimation may be performed inunits of ¼ pixels, and thus, the distance between a pair of adjacentpixels may be 4. Therefore, if a pixel at a point (4,−12) is determinedto have been moved to (4+mv_(x2)+Δx, −12+mv_(y2)+Δy) based on an affinemodel, the pixel may be determined to have the same displacement (Δx,Δy)at any arbitrary block location. This is very important for thereduction of computation because, according to the present invention, itis possible to easily obtain an affine model simply using eight inversematrices respectively corresponding to blocks 0 through 7 without theneed to calculate the inverse matrix of matrix A.

An affine model for each of blocks 1 through 7 may be obtained using thesame method used to obtain the affine model for block 0.

Once the affine models for blocks 1 through 7 are all obtained, motioncompensation may be performed on the current block, as indicated byEquation (7):

x′=round(ax+by+c)

y′=round(dx+ey+f)  (7)

In short, if a current block includes an affine-transformation object,affine transformation-based motion compensation may be performed on thecurrent block, thereby maintaining high encoding efficiency.

A video decoding method according to an exemplary embodiment of thepresent invention may be performed by inversely performing theabove-mentioned video encoding method. That is, it may be determinedwhether an affine-transformation object exists in a reference block.Thereafter, if an affine-transformation object exists in the referenceblock, a predicted block may be generated by performing affinetransformation-based motion compensation on the reference block. On theother hand, if no affine-transformation object exists in the referenceblock, a predicted block may be generated by performing motionvector-based motion compensation on the reference block. Thereafter, acurrent block may be generated using a predicted block and a residualsignal included in a video signal to be decoded. Therefore, a videodecoding apparatus according to an exemplary embodiment of the presentinvention, unlike a typical video decoding apparatus, may include anaffine-transformation object calculation unit determining whether anaffine-transformation object exists in the reference block.

The video encoding and decoding methods according to the presentinvention are not restricted to the exemplary embodiments set forthherein. Therefore, variations and combinations of the exemplaryembodiments set forth herein may fall within the scope of the presentinvention.

The present invention can be realized as computer-readable code writtenon a computer-readable recording medium. The computer-readable recordingmedium may be any type of recording device in which data is stored in acomputer-readable manner Examples of the computer-readable recordingmedium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disc,an optical data storage, and a carrier wave (e.g., data transmissionthrough the Internet). The computer-readable recording medium can bedistributed over a plurality of computer systems connected to a networkso that computer-readable code is written thereto and executed therefromin a decentralized manner. Functional programs, code, and code segmentsneeded for realizing the present invention can be easily construed byone of ordinary skill in the art.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

INDUSTRIAL APPLICABILITY

The present invention can be effectively applied to the encoding ordecoding of a video signal and can thus achieve high efficiencyespecially when a block to be encoded includes an affine-transformationobject having an affine transformation such as rotation, enlargement orreduction.

1. A video encoding method comprising: determining whether a current block includes an affine-transformation object having an affine transformation; if the current block includes an affine-transformation object, generating a prediction block by performing affine transformation-based motion compensation on the current block in consideration of an affine trans-formation of the affine-transformation object; and if the current block does not include any affine-transformation object, generating a prediction block by performing motion vector-based motion compensation on the current block using a motion vector of the current block.
 2. The video encoding method of claim 1, further comprising generating a differential signal based on a difference between the current block and the prediction block.
 3. The video encoding method of claim 2, further comprising generating a bitstream including data obtained by encoding the differential signal.
 4. The video encoding method of claim 1, further comprising calculating the motion vector of the current block with reference to a reference block.
 5. The video encoding method of claim 1, further comprising, if the current block includes an affine-transformation object and is located on the upper left corner of a frame, performing affine transformation-based motion compensation on the current block.
 6. The video encoding method of claim 1, further comprising, if the current block includes an affine-transformation object, one of a number of blocks adjacent to the current block is intra-encoded, and the current block references a different reference block from the adjacent blocks, performing motion vector-based motion compensation on the current block.
 7. The video encoding method of claim 1, further comprising, if the current block includes an affine-transformation object and a maximum of the angles between the motion vector of the current block and the motion vectors of a number of blocks adjacent to the current block is greater than a reference value, performing motion vector-based motion compensation on the current block.
 8. The video encoding method of claim 1, further comprising, if the current block includes an affine-transformation object and a maximum variation of the affine-transformation object is greater than a reference value, performing motion vector-based motion compensation on the current block.
 9. The video encoding method of claim 1, wherein the performing of affine transformation-based motion compensation comprises dividing the current block into a number of triangular blocks and applying different affine models to the triangular blocks.
 10. A video encoding apparatus comprising: a motion estimation unit calculating a motion vector of a current block with reference to a reference block; an affine-transformation object calculation unit determining whether a current block to be subjected to motion compensation includes an affine-transformation object having an affine transformation and outputting an affine-transformation object detection signal corresponding to the results of the determination; and a motion compensation unit generating a prediction block by performing either affine transformation-based motion compensation or motion vector-based motion compensation on the current block in response to the affine-transformation object detection signal.
 11. The video encoding apparatus of claim 10, further comprising a differential unit generating a differential signal based on a difference between the current block and the prediction block.
 12. The video encoding apparatus of claim 11, further comprising an encoding unit generating a bitstream including data obtained by encoding the differential signal.
 13. A video decoding method comprising: determining whether an affine-transformation object exists in a reference block; if an affine-transformation object exists in the reference block, generating a predicted block by performing affine transformation-based motion compensation on the reference block; and if no affine-transformation object exists in the reference block, generating the predicted block by performing motion vector-based motion compensation on the reference block.
 14. The video decoding method of claim 13, further comprising generating a residual signal and a motion vector for performing motion compensation on the reference block by reconfiguring the bitstream of an input video signal.
 15. The video decoding method of claim 14, further comprising generating a current block based on the predicted block and the residual signal.
 16. The video decoding method of claim 13, wherein the performing of affine transformation-based motion compensation comprises dividing the current block into a number of triangular blocks and applying different affine models to the triangular blocks.
 17. A video decoding apparatus comprising: an affine-transformation object detection unit determining whether an affine-transformation object exists in a reference block and outputting a signal indicating the results of the determination; a motion compensation unit generating a predicted block by performing one of affine transformation-based motion compensation and motion vector-based motion compensation on the reference block in response to the signal output by the affine-transformation object detection unit; and an adding unit which generates a current block by adding the predicted block and a residual signal.
 18. The video decoding apparatus of claim 17, further comprising a decoding unit generating a residual signal and a motion vector for performing motion compensation on the reference block by reconfiguring the bitstream of an input video signal.
 19. A computer-readable recording medium having recorded thereon a program for executing a video encoding method comprising: determining whether a current block includes an affine-transformation object having an affine transformation; if the current block includes an affine-transformation object, generating a prediction block by performing affine transformation-based motion compensation on the current block in consideration of an affine trans-formation of the affine-transformation object; and if the current block does not include any affine-transformation object, generating a prediction block by performing motion vector-based motion compensation on the current block using a motion vector of the current block.
 20. A computer-readable recording medium having recorded thereon a program for executing a video decoding method comprising: determining whether an affine-transformation object exists in a reference block; if an affine-transformation object exists in the reference block, generating a predicted block by performing affine transformation-based motion compensation on the reference block; and if no affine-transformation object exists in the reference block, generating the predicted block by performing motion vector-based motion compensation on the reference block. 